In the past, when, for example, a thin plate-like workpiece such as a silicon wafer is flattened, a double-side polishing apparatus or a double-side lapping apparatus has been used. For example, the double-side polishing apparatus has a disk-shaped carrier with a planet gear at the outer edge thereof between upper and lower turn tables to which a polishing pad formed of urethane foam or a nonwoven fabric is attached. By holding a workpiece in a holding hole of this carrier and mutually rotating a sun gear and an internal gear which engage the planet gear, the rotation and orbital motion of the carrier are generated. By this rotation and orbital motion and the rotation of the upper and lower turn tables and the sliding motion of the upper and lower turn tables and the workpiece, the upper and lower surfaces of the workpiece are polished at the same time. During polishing, in order to perform polishing efficiently, polishing slurry is supplied from a plurality of holes provided in the upper turn table.
The upper turn table is provided with an up-and-down motion mechanism and, in a position to which the upper turn table is moved upward, the carrier is disposed and a workpiece is held by the carrier. There are a case where holding of the workpiece is performed manually by an operator and a case where holding of the workpiece is performed by using an automatic handling apparatus (refer to, for example, Patent Document 1). After the workpiece is held, the upper turn table is moved downward, whereby the workpiece and the carrier are interposed between the upper and lower turn tables.
In order to control the polishing rate, there are a method of changing the sliding rate of the workpiece and the upper and lower turn tables by changing the rotation rates of the upper and lower turn tables, the sun gear, and the internal gear and a method of controlling a polishing load.
An upper turn table holding section is usually provided with a measuring instrument that measures the weight of the upper turn table. For example, when the upper turn table is in a position to which the upper turn table is moved upward, the measuring instrument measures the total weight of the upper turn table. In a position in which the upper turn table is moved fully downward, since the total weight of the upper turn table is applied to the workpiece and the carrier, the weight of the upper turn table measured by the measuring instrument becomes zero. When the upper turn table is gradually moved upward from the position in which the upper turn table is moved fully downward, the weight of the upper turn table applied only to the workpiece and the carrier starts to be gradually supported by the upper turn table holding section. That is, by appropriately controlling the height position of the upper turn table, it is possible to apply a desired polishing load to the workpiece and the carrier.